The present invention relates to an organic luminous device material comprising a 1,2,4-oxadiazole compound. Furthermore, the invention also relates to an organic luminous device using the material.
At present, the researches and developments of various display devices have been actively made. Regarding organic luminous devices, particularly, various systems have been examined, and many ideas have been proposed. In particular, organic electroluminescence (EL) devices are receiving attention as promising display devices because they can emit light of high luminance with low voltage. For example, EL devices having organic thin layers formed by vapor deposition of organic compounds are known (Applied Physics Letters, 51, p.913 (1987)). The organic EL devices described in the above literature have a laminated structure of an electron transport material and a hole transport material, and show substantial improvements in their luminescence characteristics over conventional single-layer devices.
The electron transport material used in those devices of lamination type, specifically the hydroxyquinoline-aluminum complex (hereinafter abbreviated as xe2x80x9cAlqxe2x80x9d), is one of the most effective electron transport materials. However, Alq fluoresces a green light, so that it is not suitable for producing blue luminous devices and white luminous devices. In addition, Alq is unsuitable for organic EL devices of coated type because of its extremely low solubilities in organic solvents.
As electron transport materials capable of taking the place of Alq, the use of heterocyclic compounds has been considered. With respect to the techniques of using 1,3,4-oxadiazole compounds or 1,3,4-triazole compounds as electron transport materials, various compounds and the examination results thereof have been reported as described, for example, in the 6th Lecture Preprint by the Organic molecules-bioelectronics Division of Japanese Society of Applied Physics, pp. 11-19, pp. 31-41 and pp. 53-61 (1997).
As a result of the studies made by the present inventor on the above-mentioned compounds, it turned out that those compounds still failed to provide organic EL devices having high luminance and stability, as compared to Alq. Particularly, in case where those compounds are applied to organic EL devices of coated type, they had a problem of being liable to separate out from the coated layer because of their poor solubilities. This problem is directed not only to organic EL devices but also to the whole Organic luminous devices, and hence the dissolution thereof has been desired.
Therefore, a first object of the invention is to develop heterocyclic compounds having good electron transport capability and to develop an organic luminous device material suitable for the production of an organic luminous device having high luminance.
A second object of the invention is to develop an organic luminous device material having excellent solubility and suitability for the production of an organic luminous device having a long life even when the device is produced using a coating technique. In particular, the development of an organic EL device of excellent quality is aimed at by the invention.
Other objects and effects of the present invention will become apparent from the following description.
The above-described objectives of the present invention have been achieved by providing the following materials for an organic luminous device and organic luminous devices.
1) A material for an organic luminous device, which comprises a 1,2,4-oxadiazole compound represented by formula (1) or a precursor thereof, or comprises a homopolymer or copolymer produced from monomers comprising at least one monomer unit derived from said 1,2,4-oxadiazole compound represented by formula (1): 
wherein R1 and R2 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a heterocyclic group.
2) The material according to the above 1), wherein R1 and R2 in formula (1) each independently is an aryl group or a heterocyclic group.
3) The material according to the above 1), wherein either or both of R1 and R2 is substituted with a fluorine atom or a substituent containing a fluorine atom.
4) An organic luminous device comprising a material according to the above 1).
5) The organic luminous device according to the above 4), which comprises a coated organic layer, wherein said coated organic layer contains said material.
The compound represented by formula (1) is described in detail below.
R1 and R2 each independently represents a hydrogen atom, an alkyl group (preferably containing 1 to 30 carbon atoms, more preferably 1 to 15 carbon atoms, particularly preferably 1 to 8 carbon atoms, with examples thereof including methyl, t-butyl and cyclohexyl groups), an alkenyl group (preferably containing 2 to 30 carbon atoms, more preferably 2 to 15 carbon atoms, particularly preferably 2 to 8 carbon atoms, with examples thereof including vinyl, 1-propenyl, 1-butene-2-yl and cyclohexene-1-yl groups), an alkynyl group (preferably containing 2 to 30 carbon atoms, more preferably 2 to 15 carbon atoms, particularly preferably 2 to 8 carbon atoms, with examples thereof including ethynyl and 1-propynyl groups), an aryl group (preferably containing 6 to 30 carbon atoms, more preferably 6 to 15 carbon atoms, particularly preferably 6 to 12 carbon atoms, with examples thereof including phenyl, tolyl, xylyl, naphthyl, biphenyl and pyrenyl groups) or a heterocyclic group (preferably a 5- or 6-membered heterocyclic group, which may be fused together with another ring, containing a nitrogen, oxygen or sulfur atom as a hetero atom in addition to 1 to 30 carbon atoms, preferably 2 to 15 carbon atoms, more preferably 2 to 8 carbon atoms, with examples thereof including pyridyl, piperidyl, oxazolyl, oxadiazolyl, tetrahydrofuryl and thienyl groups). Of these, aryl groups and heterocyclic groups are particularly preferred. These groups may further have substituents.
Examples of the substituent which can be contained in the groups represented by R1 and R2 include an alkyl group (preferably containing 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, with examples thereof including methyl, ethyl, iso-propyl, tert-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl, cyclopentyl and cyclohexyl groups), an alkenyl group (preferably containing 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, with examples thereof including vinyl, allyl, 2-butenyl and 3-pentenyl groups), an alkynyl group (preferably containing 2 to 20 carbon atoms, more preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, with examples thereof including propargyl and 3-pentynyl groups), an aryl group (preferably containing 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, with examples thereof including phenyl, p-methylphenyl and naphthyl groups), an alkoxy group (preferably containing 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, with examples thereof including methoxy, ethoxy, butoxy, tert-butoxy, 2-ethylhexyloxy and dodecyloxy groups), a substituted carbonyl group (preferably containing 2 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, with examples thereof including acetyl, benzoyl, methoxycarbonyl, phenyloxycarbonyl, dimethylamino-carbonyl and phenylaminocarbonyl groups), an amino group (preferably containing 0 to 20 carbon atoms, more preferably 2 to 16 carbon atoms, particularly preferably 2 to 12 carbon atoms, with examples thereof including dimethylamino, methylcarbamoyl, ethylsulfonylamino, dimethylaminocarbonylamino and phthal-imido groups), a sulfonyl group (preferably containing 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, with examples thereof including mesyl and tosyl groups), -a sulfo group, a carboxyl group, a heterocyclic group (preferably containing a nitrogen, oxygen or sulfur atom as a hetero atom in addition to 1 to 50 carbon atoms, preferably 1 to 30 carbon atoms, more preferably 2 to 12 carbon atoms, with examples thereof including imidazolyl, pyridyl, furyl, piperidyl, morpholino, benzoxazolyl and triazolyl groups), a hydroxyl group, an aryloxy group (preferably containing 6 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, particularly preferably 6 to 12 carbon atoms, with examples thereof including phenoxy and naphthyloxy groups), a halogen atom (preferably fluorine, chlorine, bromine or iodine atom, particularly preferably fluorine atom), a thiol group, an alkylthio group (preferably containing 1 to 20 carbon atoms, more preferably 1 to 16 carbon atoms, particularly preferably 1 to 12 carbon atoms, e.g., methylthio), an arylthio group (preferably containing 6 to 20 carbon atoms, more preferably 6 to 16 carbon atoms, particularly preferably 6 to 12 carbon atoms, e.g., phenylthio) and a cyano group. Of these substituents, the alkyl, aryl, heterocyclic and alkoxy groups and a fluorine atom are preferred. In particular, it is preferred that the compound has at least one fluorine atom or a substituent having at least one fluorine atom (e.g., fluoromethyl, trifluoromethyl, perfluorooctyl).
The 1,2,4-oxadiazole compounds represented by formula (1) can be synthesized using known methods. In general, those compounds can be synthesized by heating aliphatic or aromatic nitrites together with excess hydroxylamine in an alcohol-water mixed solvent to convert it to the corresponding amidoximes, and then making the amidoximes react with esters, acid halides or acid anhydrides in a condition that the amidoximes are dissolved in absolute alcohol and dissociated by the use of a metal alkoxide as a base.
Accordingly, the 1,2,4-oxadiazole compounds may be synthesized in such a manner that the amidoximes as precursors thereof are incorporated together with esters, acid halides or acid anhydrides in the organic layer of an organic luminous device and these they are made to react with each other inside the organic layer, e.g., by applying heat thereto.
The monomer units derived from the 1,2,4-oxadiazole compounds include two embodiments. In one embodiment, the compound constitutes a monomer unit by itself. In the other embodiment, on the other hand, the compound and a polymerizable unsaturated compound (e.g., a vinyl compound) combine to constitute a monomer unit. Examples of the monomer unit of the latter embodiment include the monomer units derived from polymerizable ethylenic unsaturated compounds, such as (meth)acrylic acid (esters) and (meth)acrylamides.
In the invention, homopolymers formed from these monomer units alone and copolymers formed from these monomer units and other copolymerizable unsaturated compounds (the representatives of which are the vinyl compounds as recited above) can be used. The number-average molecular weight of the (co)polymer used as an organic luminous device material is preferably not higher than 1.00xc3x97106 preferably from 1xc3x97104 to 2.0xc3x97105.
The 1,2,4-oxadiazole compounds and the polymers derived therefrom according to the present invention can be used in a combination of two or more thereof.